1. Field of the Invention
This invention relates to a method for manufacturing a diaphragm for use in an electroacoustic transducer (hereinafter also referred to as an electroacoustic-transducer-use), and more particularly to a method for manufacturing an electroacoustic-tranducer-use diaphragm in a multi-layer structure including a first diaphragm layer of synthetic resin molded in a predetermined shape by injection molding and a second diaphragm layer (skin layer) layered or stacked in intimate contact on the first diaphragm layer and made of a different material from the first diaphragm layer.
2. Description of the Related Art
The physical properties required for the electroacoustic-tranducer-use diaphragm such as a speaker or microphone are large specific modulus (E/ρ) or specific bending modulus (E/ρ3), suitable internal loss, endurance to mechanical fatigue and good weatherability. Further, in recent years, moisture resistance is also an important property for mainly a vehicle application.
In order to satisfy these demands, as the material for the diaphragm, metal, ceramics, synthetic resin, synthetic fiber, natural cellulose fiber, etc. have been proposed. In recent years, various raw materials such as a microbe cellulose fiber made by biotechnology have been also proposed. The materials thus proposed have been machined by various machining techniques.
However, each raw material has its own property. The raw materials proposed have merits and demerits from the standpoint of view of the physical property of the diaphragm. Therefore it is actually difficult to cause the diaphragm formed of a single material to exhibit many physical properties required as the diaphragm in good balance.
For example, “paper diaphragm” using the cellulose fiber such as wooden pulp as the raw material is relatively light in weight, and has an appropriate elasticity and internal loss. The paper diaphragm presented merits of being manufactured by various techniques and of high freedom of design, but presented demerits of difficulty of assuring the waterproof and of providing high elasticity to ensure high input endurance.
On the other hand, the synthetic-resin diaphragm or metallic diaphragm has merits of easiness of assuring the waterproof and of providing the high elasticity to ensure high input endurance, but demerits of a high density and small internal loss. Therefore, the synthetic-resin diaphragm and metallic diaphragm are not optimum as the diaphragm for a low-to-midi range or all bands which requires light weight and high rigidity.
In view of the above circumstances, it has been proposed to provide the diaphragm with a good balance in the physical properties by adopting a multi-layer structure consisting of a plurality of raw materials with different physical properties to compensate for the demerits of the individual raw materials.
FIG. 1 shows an example of such a diaphragm for use in an electroacoustic transducer.
An electroacoustic-transducer-use diaphragm 1 illustrated herein has a double layer structure consisting of a first diaphragm layer 3 made of synthetic resin molded in a predetermined shape by injection molding and a second diaphragm layer (skin layer) 5 layered in intimate contact on the first diaphragm layer 3 and made of a different material from the first diaphragm layer 3.
By compensating for the demerit of e.g. woven cloth of aramid fiber used as a raw material of the second diaphragm layer 5 by the characteristic of the resin layer, the diaphragm having various physical properties in good balance can be obtained.
Meanwhile, as a method for manufacturing such an elecroacoustic-transducer-use diaphragm in a multi-layer structure, there has been proposed a method in which after the first diaphragm layer 3 and the second diaphragm layer 5 have been individually made, both layers are integrated using e.g. adhesive as required or another method in which with the second diaphragm layer 5 having been previously molded in a predetermined size/shape by a separate press molding machine, the second diaphragm layer 5 thus molded is insert-molded in molding the first diaphragm layer 3 so that it is integrated to the first diaphragm layer 3 (e.g. see JP-A-2000-4496).
However, the above conventional method has a problem that the number of manufacturing steps is increased because of the step of independently molding the second diaphragm layer 5, thus increasing the production cost.
Further, when the second diaphragm layer 5 molded is set in a die for injection-molding the first diaphragm layer 3 (hereinafter referred to as an injection-molding die), or when the first diaphragm layer 3 and the second diaphragm layer 5 which have been individually made are stacked, it was difficult to provide uniform contact over the entire region of a stacking plane because of a fine size error therebetween and was impossible to ensure a uniform physical property over the entire region of the diaphragm, thus giving possibility of occurrence of changes in the acoustic characteristic.
The problems that this invention intends to solve are the problems involved in the above conventional technique, for example, a problem of an increase in cost due to the increase in the number of manufacturing steps and a problem of partial fluctuation in intimate contact due to a size error between the first diaphragm layer and the second diaphragm layer, thus leading to a fluctuating vibrating characteristic.